(1) Field Of The Invention
The invention relates generally to devices and systems for discrete computer controlled small-quantity deposition of viscous a material at a succession of X Y locations on a surface. More specifically, the invention relates to such devices with additional apparatus for discrete control of the height of the dispensing needle orifice (or orifices) over the surface irrespective of surface height variations, and for discrete orientation of multiple needle orifices in the plane of the surface at each X Y location.
(2) Description of The Prior Art
In the prior art, systems of the general computer positioning type are known and have been used to deposit small quantities of viscous material such as solder flux, a slurry of such flux with solder particles or a solder masking material according to a computer directed program successively positioning a needle orifice over each preselected location on a surface such as an electronic printed circuit board. Two particularly pertinent devices and systems are disclosed in U.S. Pat. Nos. 4,584,964 and 4,572,103. Both of these patents have the same inventorship and ownership as this application and the inventive subject matter described herein.
U.S. Pat. No. 4,584,964 describes a system of the computer controlled type which employs a controlled valve for passing a predetermined quantity of the viscous material to be deposited at each discrete location on the surface over which its needle orifice is successively positioned. That disclosure particularly includes novel means for drawback (anti-drip) from the needle orifice. However, it does not address the problem of vertical needle orifice positioning over a less than completely regular and planar surface. The needle orifice height (Z coordinate) is uniformly programmed to a valve which is only optimum if the surface is flat and extremely smooth. Since devices of this type deposit very small quantities at each discrete location, optimization of Z coordinate is important and cannot be programmed along with the successive X and Y coordinates, because each circuit board or other surface is likely to contain its own unique variation, warp or distortions.
In the device of U.S. Pat. No. 4,572,103 the deposition of the viscous material is via a pumping valve (force piston thrusting within a cylinder). This configuration is better adapted to the handling of solder particle slurry materials than is the controlled valve version of U.S. Pat. No. 4,584,964 because of the relatively large effective pressure applied to the needle by the force piston. That pressure does not affect the apparatus "upstream" from the force piston cylinder.
Systems of the prior art, including those described in the referenced U.S patents find their greatest application in production set-ups where a number of circuit board units of the same configuration are being prepared for solder application by flow soldering or other known techniques. The computerized flux or slurry deposition is very rapidly accomplished. The economics of manufacture of such circuit boards demands that costs be minimized and that fabrication be performed by relatively low skill operators and automatic equipment.
The aforemention U.S. patents discuss other prior art extant in this general art, such as U.S. Pat. Nos. 3,731,648 and 3,785,898 which show the general type of computerized X, Y and Z axis positioning which is an element of the combination of this invention as well as of the systems of U.S. Pat. Nos. 4,584,964 and 4,572,103 discussed hereinbefore.
None of the known systems of the type described provides a solution to the problem of circuit board warp and surface Z axis perturbations. Moreover, since the deposition of a single bead or cone of viscous material at a time is contemplated by the known apparatus, there is room for improvement and corresponding production time reduction.
The invention herein described deals in unique ways with both the circuit board variations and need for increased speed of operation in accordance with unique advancements in this art which will be described as this specification proceeds.